What is the proper workflow when adding an image texture to a material
I don't believe that this matters, as long as you keep in mind that there is both an Image texture and a UV Map involved. 

The UV/Image editor knows that there is a link to an image, and so does the node editor, as you can select them both from the image texture dropdown in either place. Blender knows the image is there.

On the flip side, I know that certain things like texture baking requires there to be a present reference to an image texture in node form on the material you are going to bake to (Although it does not need to be linked to anything for it to work).

For UV purposes however, you have to realize that the UV map is just texture coordinates of the verts that make up the faces of your geometry. So for Blender there is no real technical need to even display an image to get some sort of UV map via the Unwrap functions because they automatically get placed somewhere, however for the user this is visually crucial, so you can modify them to fit your needs.

In other words, It's the end result that truly matters.

For some, they like to attempt to get a good feel for the mapping upfront and let it influence their topology, while for others, they like to ignore it until they are done getting their geometry tuned and then making the map fit the geometry. For others they do both. This is just a matter of preference, as there is nothing in the software (from what I can tell) constraining the freedom to choose how you want to go about this. There are also times to not worry about it, because you just want to brush paint your texture directly onto your mesh (then this would require that you save your painted image and reference in the node editor, but UV is pretty much automatic in this case.

A texture is still a texture, and a UV Map is the channel/conduit by which the geometry displays (stretches/ignores/skews/etc...) that texture per face.

If at anytime, you decide to straiten out how your geometry is mapping to this image texture, you can start or redo your UV Unwrapping, tweak the verts in the UV editor etc...

Hope this was thorough enough.